Invasive species are huge threat to the ecosystems along the St. Lawrence River and Great Lakes. Save The River’s Clean-Up the Ballast Campaign is focused on stopping aquatic invasive species introductions by tackling the primary source – ship ballast tanks.

The pace of invasive species being discovered in the Great Lakes peaked about a decade ago, when a new invader was detected, on average, more than once a year.

To stanch the onslaught, starting in 2008 all Great Lakes-bound overseas vessels were required to flush their ballast tanks in mid-ocean to expel any ballast dwelling organisms, or kill them with a blast of saltwater. No new invader has been detected in the lakes since — a point shipping industry advocates are quick to tout.

Research shows that a saltwater ballast flush can go a long way in killing most freshwater tank dwellers. But most biologists don’t think that’s enough because even if flushing ballast tanks with saltwater eliminates 98 or even more than 99% of certain classes of hitchhikers, boats arriving from ports around the globe are far from sterile.

One Great Lakes-bound freighter can carry enough ballast to fill 10 Olympic-size swimming pools. These tanks can hold not only water but also swamps of sediment that can be teeming with all manner of organisms in all different life stages, from fish eggs to microscopic zooplankton to dormant cysts that evolved over millions of years to survive most anything nature can toss at them.

A 2011 federal report looking at the threat of ballast water to all U.S. ports noted that a study conducted in Australia revealed that sediments from just one freighter ballast tank can harbor up to 300 million viable cysts of primitive dinoflagellates, which scientists dub the “cells from hell” because they can produce a deadly neurotoxin. So a flush that eliminates 99% of this ballast tank’s inhabitants could still carry 3 million potential invaders

That’s just one ballast tank, and that’s just one species.

UWM’s Strickler says there are plenty of freshwater organisms that will indeed wither when hit with a blast of saltwater.

But he considers these species pushovers. He works with animals that, depending on their life stage, can withstand everything from water fresh enough to drink to brews far brinier than the ocean.

“Most of my animals can survive salinity,” Strickler says with a wry smile as he slowly closes his eyes, “they just go to sleep.”

Most biologists, meanwhile, believe it is naïve to think the ballast problem has been solved simply because it’s been several years since a new lake invader has been detected. Sleeper colonies can lurk for years — even decades — before their numbers grow big enough to get noticed. Great Lakes species discoveries also tend to be utterly accidental — a fisherman hauls up a strange cluster of slimy critters coating his nets; students doing a routine survey of a lake bottom stumble upon something their professor doesn’t recognize.